Medical implant threaded plug having a start structure

ABSTRACT

A medical implant assembly including a receiver and a fastener. The receiver having helically wound thread extending up to a top surface thereof. The fastener having an axis of rotation and a continuously helically wound thread form. The continuously helically wound thread form having a start structure and an upper loading surface extending between a root and a crest of the continuously helically wound thread form. The start structure having a leading face extending below the upper loading surface. The leading face including a partial curvate surface extending between the root and the crest. The start structure being configured as a single lead start structure and a dual lead start structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/476,652, filed Sep. 16, 2021, which is a continuation ofU.S. patent application Ser. No. 17/123,499, filed Dec. 16, 2020, nowU.S. Pat. No. 11,129,646, which is a continuation of U.S. patentapplication Ser. No. 16/779,304, filed Jan. 31, 2020, now U.S. Pat. No.10,898,233, which is a continuation of U.S. patent application Ser. No.15/964,502, filed Apr. 27, 2018, now U.S. Pat. No. 10,548,641, which isa continuation of U.S. patent application Ser. No. 15/469,076, filedMar. 24, 2017, now U.S. Pat. No. 9,956,004, which is a continuation ofU.S. patent application Ser. No. 14/566,356, filed Dec. 10, 2014, nowU.S. Pat. No. 9,636,146, which is a continuation of U.S. patentapplication Ser. No. 13/694,849, filed Jan. 10, 2013, now U.S. Pat. No.8,911,479, issued Dec. 16, 2014, which claims the benefit of U.S.Provisional Application No. 61/631,746, filed Jan. 10, 2012 and U.S.Provisional Application No. 61/634,361, filed Feb. 28, 2012, all ofwhich are incorporated by reference herein in their entireties for allpurposes.

BACKGROUND OF THE INVENTION

The present invention is directed to structure for joining togetherparts of a medical implant, in particular to closure mechanisms for usewith open bone anchors in spinal surgery, and in some embodimentsthereof, for use with spinal bone anchors such as polyaxial screws.

Bone anchors, such as bone screws and hooks are utilized in many typesof spinal surgery in order to secure various implants to vertebrae alongthe spinal column for the purpose of stabilizing and/or adjusting spinalalignment. For example, the most common mechanism for providingvertebral support is to implant bone screws into certain bones whichthen in turn support a rod or are supported by the rod. Although bothclosed-ended and open-ended bone anchors are known, open-ended anchorsare particularly well suited for connections to longitudinal connectingmembers such as hard, soft or deformable rods, dynamic or elasticconnectors and connector arms, because such rods or other connectormembers do not need to be passed through a closed bore, but rather canbe laid or urged into an open channel within a receiver or head of sucha bone anchor. Generally, the anchors must be inserted into the bone asan integral unit or a preassembled unit, in the form of a shank or hookand connected pivotal receiver. In some instances, a portion of such apreassembled unit, such as a shank of a polyaxial bone screw assembly,may be independently implanted into bone, followed by push- or pop-onassembly of a receiver portion of the unit.

Typical open-ended bone screws include a threaded shank with a head orreceiver having a pair of parallel projecting branches or arms whichform a yoke with a U-shaped slot or channel to receive a rod or otherlongitudinal connecting member. Hooks and other types of connectors, asare used in spinal fixation techniques, may also include similar openends for receiving rods or portions of other fixation and stabilizationstructure. The open-ended head or rod receiver portion of such implantstypically includes a pair of spaced arms forming a channel closed by aclosure member after the rod or other longitudinal connecting member isplaced in the channel. Known closures include slide-on types, twist-onvarieties that are rotated ninety degrees to a locked in position, and avariety of single start helically wound guide and advancement structuresincluding, for example, thread forms having v-thread, reverse-anglebuttress or square thread forms, to name a few, as well as othernon-threadlike helically wound forms. Sometimes threaded plugs areutilized with outer threaded nuts to prevent splaying of the receiverarms.

As indicated above, the force required to press a closure structure downonto a rod or other connector located between arms of an open implant isconsiderable. Even though a head or receiver portion of an openpolyaxial bone anchor may be pivoted in a direction to make it easierfor the arms of the open implant to receive a rod or other connector,spinal misalignments, irregularities and the placement of other surgicaltools make it difficult to place the rod or other connector between thearms of the implant while a closure structure is mated with the openimplant as well as used to push the rod or other connector downwardlyinto the implant. For example, when the closure is a cylindrical plughaving a single start helically wound guide and advancement structure,such structure must be aligned with mating structure on one of theimplant arms and then rotated until a portion of the structure iscaptured by mating guide and advancement structure on both arms of theimplant, all the while the closure is being pressed down on the rodwhile other forces are pushing and pulling the rod back out of theimplant. Integral or mono-axial open implants that cannot be pivoted toreceive the rod are even more difficult to manipulate during the initialplacement of the rod and initial mating rotation of a closure plugbetween the spaced, open arms of the implant. Therefore, extraordinaryforces are placed on the implant and closure plug while the surgeoneither pushes down on the rod or pulls up on the bone to get the rod inposition between the implant arms and to initially push down upon therod with the closure plug.

SUMMARY OF THE INVENTION

A closure structure, top or plug of the invention for insertion betweenspaced arms of an open medical implant includes one or more helicallywound guide and advancement features, each feature having a startsurface or structure located at or near a bottom surface of the closureplug, each start structure simultaneously engaging and being captured byeach of the spaced arms of the open implant upon initial rotation of theclosure structure with respect to the open implant arms. According to anaspect of the invention, a double-start closure is disclosed having twohelically wound forms thereon, each form having a start structure forsimultaneously engaging a mating helical form on a respective openimplant arm. Each time the illustrated duel- or double-start closureplug is rotated one turn (three hundred sixty degrees) between theimplant arms, the closure plug advances axially into the implant andtoward the rod by a width of two helical forms. The helically woundforms of the multi-start closure spiral around a cylindrical plug bodythereof to an extent that the closure rotates over ninety degrees tofully or substantially receive the entire closure plug between the armsof the open implant. The illustrated closure is sized for at least onecomplete rotation (three hundred sixty degrees) of the plug with respectto the open implant to substantially receive the plug between theimplant arms. Multi-start closures of the invention may have two or morecoarse or fine helical forms, resulting in fewer or greater forms peraxial distance spiraling about the closure plug body and thus resultingin plugs that rotate less (when more coarse) or more (when thin or fine)than one complete rotation to be fully received between the implantarms, typically, at least a ninety-one degree rotation is preferred.

An illustrated multi-start closure and mating open implant is in theform of non-threaded, interlocking flange forms. Also disclosed aremulti-start closure structures provided with helically wound forms ofother geometry, including, but not limited to helically wound threadssuch as reverse angle, buttress, square and v-threads. The multi-startclosure may be cannulated for minimally invasive surgical applications.

Another illustrated multi-start closure embodiment of the invention isshown with a bone screw assembly having an open receiver with a pair ofopposed arms, each arm having guide and advancement structure forsimultaneous mating engagement with a start of the helically woundmulti-start closure. A further embodiment according to the inventionincludes an open bone anchor receiver having integral upwardly extendingbreak-off tabs that also have the guide and advancement structure formating with the multi-start closure. A further embodiment includes anattachable/detachable guide tool cooperating with such a multi-startopen receiver, the tool having inner guide and advancement structureslocated near a bottom thereof for rotatably and matingly receiving themulti-start closure and being synchronized with the receiver guide andadvancement structure for rotating and driving the multi-start closuredownward from the guide tool to the receiver.

Objects of the invention further include providing apparatus and methodsthat are easy to use and especially adapted for the intended use thereofand wherein the tools are comparatively inexpensive to produce. Otherobjects and advantages of this invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a multi-start closureaccording to the invention.

FIG. 2 is another perspective view of the multi-start closure of FIG. 1.

FIG. 3 is a front elevational view of the closure of FIG. 1 shown with aportion of a receiver of a polyaxial bone screw according to FIG. 8, thereceiver shown in partial front elevation with portions broken away toshow the detail thereof, and further showing a rod being pressed upon bythe closure, the rod also in partial front elevation with portionsbroken away to show the detail thereof.

FIG. 4 is a reduced top plan view of the closure of FIG. 1.

FIG. 5 is a reduced bottom plan view of the closure of FIG. 1.

FIG. 6 is an enlarged front elevational view of the closure of FIG. 1with portions broken away to show the detail thereof.

FIG. 7 is a reduced cross-sectional view taken along the line 7-7 ofFIG. 6.

FIG. 8 a partial front elevational view of an open bone screw assembly,with portions broken away to show the detail thereof, including areceiver, a shank, a compression insert and also shown in engagementwith the closure top of FIG. 1 (in reduced view) and a longitudinalconnecting member in the form of a hard rod.

FIG. 9 is a front elevational view of an alternative closure of anembodiment of the invention, similar to the closure of FIG. 1, butincluding a break-off head, the alternative closure shown with a portionof a receiver of the polyaxial bone screw of FIG. 8 shown in enlargedand partial front elevation with portions broken away to show the detailthereof, and further showing a rod being pressed upon by the alternativeclosure, the rod also in partial front elevation with portions brokenaway to show the detail thereof.

FIG. 10 is another front elevational view of the closure of FIG. 9 withportions broken away to show the detail thereof.

FIG. 11 is a front elevational view of an alternative square-threadclosure of an embodiment of the invention with portions broken away toshow the detail thereof, the closure shown with a portion of a receiverof the polyaxial bone screw of FIG. 8 shown in enlarged and partialfront elevation with portions broken away to show the detail thereof,and further showing a rod being pressed upon by the alternative closure,the rod also in partial front elevation with portions broken away toshow the detail thereof.

FIG. 12 is a front elevational view of an alternative reverse angleclosure of an embodiment of the invention with portions broken away toshow the detail thereof, the closure shown with a portion of a receiverof the polyaxial bone screw of FIG. 8 shown in enlarged and partialfront elevation with portions broken away to show the detail thereof,and further showing a rod being pressed upon by the alternative closure,the rod also in partial front elevation with portions broken away toshow the detail thereof.

FIG. 13 is a front elevational view of an alternative v-thread closureembodiment of the invention with portions broken away to show the detailthereof, the closure shown with a portion of a receiver of the polyaxialbone screw of FIG. 8 shown in enlarged and partial front elevation withportions broken away to show the detail thereof, and further showing arod being pressed upon by the alternative closure, the rod also inpartial front elevation with portions broken away to show the detailthereof.

FIG. 14 is a front elevational view of an alternative buttress-threadclosure embodiment of the invention with portions broken away to showthe detail thereof, the closure shown with a portion of a receiver ofthe polyaxial bone screw of FIG. 8 shown in enlarged and partial frontelevation with portions broken away to show the detail thereof, andfurther showing a rod being pressed upon by the alternative closure, therod also in partial front elevation with portions broken away to showthe detail thereof.

FIG. 15 is a partial front elevational view of an embodiment of amulti-start open bone anchor receiver of an embodiment of the inventionwith portions broken away to show the detail thereof, the receiverincluding break-off tabs.

FIG. 16 is an enlarged and partial front elevational view of thereceiver of FIG. 15 with portions broken away to show the detailthereof.

FIG. 17 is a partial front elevational view of an embodiment of a boneanchor receiver having a guide and advancement structure that matinglycooperates with the multi-start closure of FIG. 1, also shown in frontelevation, the receiver having portions broken away to show the detailthereof, and further shown with a guide tool, shown in phantom, theguide tool having a multi-start guide and advancement structurereceiving inner surface synchronized with the bone anchor receiver guideand advancement structure.

FIG. 18 is an exploded perspective view of the polyaxial bone screwassembly of FIG. 8.

FIG. 19 is an enlarged perspective view of the receiver of FIG. 18.

FIG. 20 is a top plan view of the receiver of FIG. 19.

FIG. 21 is a bottom plan view of the receiver of FIG. 19.

FIG. 22 is a side elevational view of the receiver of FIG. 19.

FIG. 23 is an enlarged cross-sectional view taken along the line 23-23of FIG. 20.

FIG. 24 is an enlarged cross-sectional view taken along the line 24-24of FIG. 22.

FIG. 25 is an enlarged cross-sectional view taken along the line 25-25of FIG. 20.

FIG. 26 is an enlarged perspective view of the retainer of FIG. 18.

FIG. 27 is a top plan view of the retainer of FIG. 16.

FIG. 28 is a bottom plan view of the retainer of FIG. 26.

FIG. 29 is an enlarged cross-sectional view taken along the line 29-29of FIG. 27.

FIG. 30 is an enlarged perspective view of the compression insert ofFIG. 18.

FIG. 31 is another perspective view of the insert of FIG. 30.

FIG. 32 is a top plan view of the insert of FIG. 30.

FIG. 33 is a bottom plan view of the insert of FIG. 30.

FIG. 34 is a reduced side elevational view of the insert of FIG. 30.

FIG. 35 is an enlarged cross-sectional view taken along the line 35-35of FIG. 32.

FIG. 36 is an enlarged cross-sectional view taken along the line 36-36of FIG. 32.

FIG. 37 is an enlarged front elevational view of the receiver andretainer of FIG. 18 with portions of the receiver broken away to showthe detail thereof and shown in an early stage of assembly with theretainer.

FIG. 38 is a front elevational view with portions broken away of thereceiver and retainer, similar to FIG. 37, further showing the retainerand also the compression insert of FIG. 18 in a later stage of assembly,the compression insert shown in side elevation.

FIG. 39 is a reduced front elevational view with portions broken away,similar to FIG. 38, showing the insert in a stage of being rotated intoa desired position within the receiver.

FIG. 40 is a reduced front elevational view with portions broken away,similar to FIG. 39 showing the insert being rotated into the desiredposition.

FIG. 41 is an enlarged and partial perspective view of the assembly asshown in FIG. 40, further showing portions of the receiver pressed orcrimped toward the insert to prohibit further rotation of the insertwith respect to the receiver.

FIG. 42 is an enlarged and partial, partially exploded front elevationalview of the shank of FIG. 18 and also the receiver, retainer andcompression insert of FIG. 18 as assembled as in FIG. 32, with portionsbroken away to show the detail thereof, the shank being shown implantedin a vertebra, shown in phantom, as the shank may be assembled with thereceiver either before or after implantation.

FIG. 43 is a partial front elevational view, similar to FIG. 42, withportions broken away to show the detail thereof and showing the shank ina stage of assembly with the retainer.

FIG. 44 is an enlarged partial front elevational view, similar to FIG.43, with portions broken away to show the detail thereof and showing theshank in a subsequent stage of assembly with the retainer wherein theretainer is at maximum expansion with the receiver cavity.

FIG. 45 is a reduced and partial front elevational view, similar to FIG.44, with portions broken away to show the detail thereof wherein theshank is fully assembled with the retainer.

FIG. 46 is a partial front elevational view, similar to FIG. 45, withportions broken away to show the detail thereof and showing the retainerdropped down to a seated position within the receiver.

FIG. 47 is an enlarged and partial front elevational view with portionsbroken away, similar to FIG. 46 and further showing the insert afterbeing pressed downwardly into friction fit engagement with the shank.

FIG. 48 is an enlarged and partial front elevational view with portionsbroken away of the assembly of FIG. 18, shown with the closure toppartially assembled as also shown in FIG. 3.

FIG. 49 is an enlarged and partial front elevational view with portionsbroken away, similar to FIG. 48 and further showing the closure fullyassembled between arms of the receiver.

FIG. 50 a reduced and partial front elevational view with portionsbroken away of the assembly of FIG. 49, but with the rod and closure topthereof removed and replaced with an alternative deformable rod and analternative multi-start closure of the invention, the insert remaininglocked against the receiver and thus keeping the shank locked in placeduring removal and replacement of the rod and closure top.

FIG. 51 is a reduced and partial perspective view of the assembly ofFIG. 49.

FIG. 52 is a partial perspective view, similar to FIG. 51, but showingthe shank disposed at an eighteen degree angle (cephalic) with respectto the receiver.

FIG. 53 is a partial perspective view, similar to FIG. 52, but showingthe shank disposed at an eighteen degree angle (caudal) with respect tothe receiver.

FIG. 54 is a partial perspective view, similar to FIG. 53, but showingthe shank disposed at an eighteen degree angle (lateral) with respect tothe receiver.

FIG. 55 is a partial perspective view, similar to FIG. 54, but showingthe shank disposed at a forty-two degree (medial) by eight degree(cephalic) angle with respect to the receiver.

FIG. 56 is a partial perspective view, similar to FIG. 55, but showingthe shank disposed at a forty-two degree (medial) angle with respect tothe receiver.

FIG. 57 is a partial perspective view, similar to FIG. 56, but showingthe shank disposed at a forty-two degree (medial) by eight degree(caudal) angle with respect to the receiver.

FIG. 58 is an enlarged front elevational view of the assembly of FIG. 57with portions broken away to show the detail thereof.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the bone attachment structures in actual use.

Furthermore, the terms lead, pitch and start, as such terms are used todescribe helically wound guide and advancement structures, are to beunderstood as follows: Lead is a distance along the axis of a closureplug that is covered by one complete rotation (360 degrees) of theclosure plug with respect to a mating open implant. Pitch is thedistance from a crest (or outer point or location) of one guide andadvancement structure form to the next. For example in a single-startthread-form, such as a single start, helically wound v-thread closureplug, lead and pitch are the same. Single start means that there is onlyone ridge or helically wound form wrapped around a cylindrical core, orin the case of the present invention, wrapped around a cylindricalclosure plug body and thus there is only one start structure or surfaceat a base or forward end of the closure body that initially engages amating structure on the open implant. Each time a single start closurerotates one turn (360 degrees), the closure has advanced axially by awidth of one ridge or one helical form. Double-start means that thereare two ridges or forms wrapped around a core body and thus there aretwo starting surfaces or structures on the closure plug. Therefore, eachtime a double-start body rotates one turn (360 degrees), such a body hasadvanced axially by a width of two ridges or forms. Multi-start meansthat there are at least two and may be up to three or more of suchridges or forms wrapped around a core body.

With reference to FIGS. 1-8 and 18-58, and in particular to FIGS. 8 and18, the reference number 1 generally represents an open implant in theform of a polyaxial bone screw apparatus or assembly that includes ashank 4, that further includes a body 6 integral with an upwardlyextending upper portion or capture structure 8; a receiver 10; aretaining structure or retainer 12, a compression or pressure insert 14,and a multi-start closure structure or plug 18 of the invention in theform of a cylindrical plug having a double start helically woundflange-form. It is noted that multi-start closure embodiments of theinvention, such as the closure 18 may be used with a variety of openimplants including, but not limited to a wide variety of polyaxialscrews, mono-axial or fixed screws, hooks and other types of openimplants requiring a plug or closure mechanism to fix a rod or otherimplant member to a vertebra or other bone. Thus, the assembly 1 is onlyone example of how multi-start closures of the invention may be used.

The closure structure 18 presses against and captures a longitudinalconnecting member, for example, a rod 21 which in turn engages thecompression insert 14 that presses against the shank upper portion 8that is attached to the retaining structure that in turn presses againstan inner surface of the receiver 10, so as to capture and fix thelongitudinal connecting member 21 within the receiver 10 and thus fixthe member 21 relative to a vertebra (not shown). The illustratedreceiver 10 and the shank 4 cooperate in such a manner that the receiver10 and the shank 4 can be secured at any of a plurality of angles,articulations or rotational alignments relative to one another andwithin a selected range of angles both from side to side and from frontto rear, to enable flexible or articulated engagement of the receiver 10with the shank 4 until both are locked or fixed relative to each othernear the end of an implantation procedure.

The illustrated rod 21 is hard, stiff, non-elastic and cylindrical,having an outer cylindrical surface 22. However, in other embodiments,the rod 21 may be elastic, deformable and/or of a differentcross-sectional geometry. The rod 21 may be made from a variety ofmetals, metal alloys and deformable and less compressible plastics,including, but not limited to rods made of elastomeric,polyetheretherketone (PEEK) and other types of materials, such aspolycarbonate urethanes (PCU) and polyethylenes. Furthermore, in lieu ofa rod, longitudinal connecting members for use with the assembly 1 maytake a variety of shapes, and/or may include a tensioned cord asdescribed in greater detail herein.

It is noted that the receiver 10 includes guide and advancementstructures 168 that are shown as interlocking flange forms described ingreater detail in applicant's U.S. Pat. No. 6,726,689, also incorporatedby reference herein. Alternately, when the closure structure includes adifferent helical form, the receiver cooperating structures (e.g., 168)must also be of a cooperating, mating geometry, such as a square-shapedthread receiving form, a buttress thread receiving form, a reverse anglethread receiving form or other thread-like or non-thread-like helicallywound discontinuous advancement structure receiving forms for operablyguiding under rotation and advancing a multi-start closure structuredownward between the receiver arms 160, as well as eventual torqueingwhen the closure structure abuts against the rod 21 or other connectingmember.

With particular reference to FIGS. 1-7, the illustrated multi-startclosure structure 18 is a double start closure having a substantiallycylindrical plug body 40 having an axis of rotation that is the same asthat of the receiver 10 and including a helically wound guide andadvancement structure in the form of a pair of helically wound forms 42and 43, each illustrated as an interlocking flange form that operablyjoins with mating flange form guide and advancement structures 168disposed on the arms of the receiver 10. The form 42 includes a startsurface or structure 46 and the form 43 includes a start surface orstructure 47. Each helically wound form 42 and 43 may take a variety offorms and geometries, including those described in Applicant's U.S. Pat.No. 6,726,689, which is incorporated by reference herein. It is noted(and also described in greater detail subsequently herein) that each ofthe closure structure guide and advancement structures or forms 42 and43 could alternatively be in the form of a buttress thread, a squarethread, a reverse angle thread, a v-thread or other thread like ornon-thread like helically wound advancement structures, for operablyguiding under rotation and advancing the closure structure downwardbetween the arms of the receive 10 and preferably having such a natureas to resist splaying of the receiver arms when the closure structure 18is advanced into the receiver channel. The specific flange forms 42 and43 illustrated in FIGS. 1-7, as well as acceptable alternative lockingforms, are described in detail in Applicant's U.S. Pat. No. 6,726,689,incorporated by reference herein, and thus shall not be discussedfurther herein. Such interlocking flange forms are preferred as theadded strength provided thereby beneficially cooperate with and counterany reduction in strength caused by the any reduced profile of thereceiver 10 that may more advantageously engage longitudinal connectingmember components.

The illustrated closure structure 18 also includes a top surface 54 withan internal drive 56 in the form of an aperture that is illustrated as astar-shaped internal drive such as that sold under the trademark TORX,or may be, for example, a hex drive, or other internal drives such asslotted, tri-wing, spanner, two or more apertures of various shapes, andthe like. A driving tool (not shown) sized and shaped for engagementwith the internal drive 56 is used for both rotatable engagement and, ifneeded, disengagement of the closure 18 from the receiver 10 at arms160. It is also foreseen that the closure structure 18 may alternativelyinclude a break-off head designed to allow such a head to break from abase of the closure at a preselected torque, for example, 70 to 140 inchpounds. Such a closure structure would also include a body surfacehaving an internal drive to be used for closure removal. A base orbottom surface 58 of the closure is planar and further includes a rim 60for engagement and penetration into the surface 22 of the rod 21 incertain embodiments of the invention. The closure top 18 furtherincludes a cannulation through bore 62 extending along a central axisthereof and through a drive base surface 63 and the bottom surface 58thereof. Such a through bore provides a passage through the closure 18interior for a length of wire (not shown) inserted therein to provide aguide for insertion of the closure top into the receiver arms 160.

The closure structure 18 helically wound flange form start structures 46and 47 of the respective forms 42 and 43 are located on opposite sidesof the closure plug body 40 and are both located adjacent the bottomsurface 58. As illustrated in FIG. 3, for example, when the closurestructure 18 is rotated into the receiver 10 between receiver arms 160,each having a guide and advancement structure 168, the start 46 engagesmating guide and advancement structure 168 on one arm 160 and the start47 simultaneously engages guide and advancement structure 168 on theopposing arm 160, both forms 42 and 43 being simultaneously captured bythe mating forms 168 on the opposed arms 160. As the structure 18 isrotated, the structure advances axially downwardly between the arms 160and presses evenly down upon the captured rod 21. Each time theillustrated duel- or double-start closure plug 18 is rotated onecomplete turn or pass (three hundred sixty degrees) between the implantarms, the closure plug 18 advances axially into the implant and towardthe rod by a width of two helical flange forms. The illustrated closure18 is sized for at least one complete rotation (three hundred sixtydegree) of the plug 18 with respect to the receiver 10 open arms 160 tosubstantially receive the plug between the implant arms. Each of thestart structures 46 and 47 includes a leading face having at least onecurvate surface. The at least one curvate surface includes at least oneradius of curvature. In one embodiment, the at least one curvate surfaceis both concave and convex. Multi-start closures of the invention mayhave two or more coarse or fine helical forms, resulting in fewer orgreater forms per axial distance spiraling about the closure plug bodyand thus resulting in plugs that rotate less or more than one completerotation to be fully received between the implant arms. Preferably,helically wound forms of the multi-start closure of the invention aresized so as to spiral around a cylindrical plug body thereof to anextent that the closure rotates at least ninety-one degrees to fully orsubstantially receive the closure plug between the arms of the bonescrew receiver or other open implant. Particularly preferred guide andadvancement structures are sized for at least one complete turn or pass(three-hundred sixty degree) of the closure between the receiver 10 armsand as many as two to three rotations to be fully received betweenimplant arms.

An alternative closure top, such as the top 18′ shown in FIG. 50 for usewith a deformable rod, such as a PEEK rod 21′, for example, includes abottom surface 58′ that has a domed portion 66′ with a central nub 68′in lieu of the flat and rimmed surfaces of the closure top 18.Otherwise, the closure top 18′ includes a guide and advancementstructures 42′ and 43′, a top surface 54′ and an internal drive feature56′ the same or substantially similar to the respective guide andadvancement structures 42 and 43, top surface 54 and internal drivefeature 56 of the closure top 18.

The shank 4, best illustrated in FIGS. 18 and 42-49, is elongate, withthe shank body 6 having a helically wound bone implantable thread 124(single or dual lead thread form) extending from near a neck 126 locatedadjacent to the upper portion or capture structure 8, to a tip 128 ofthe body 6 and extending radially outwardly therefrom. During use, thebody 6 utilizing the thread 124 for gripping and advancement isimplanted into the vertebra 17 leading with the tip 128 and driven downinto the vertebra with an installation or driving tool (not shown), soas to be implanted in the vertebra to near the neck 126, as more fullydescribed in the paragraphs below. The shank 4 has an elongate axis ofrotation generally identified by the reference letter A.

The neck 126 extends axially upward from the shank body 6. The neck 126may be of the same or is typically of a slightly reduced radius ascompared to an adjacent upper end or top 132 of the body 6 where thethread 124 terminates. Further extending axially and outwardly from theneck 126 is the shank upper portion 8 that provides a connective orcapture apparatus disposed at a distance from the upper end 132 and thusat a distance from the vertebra 17 when the body 6 is implanted in suchvertebra.

The shank upper portion 8 is configured for a pivotable connectionbetween the shank 4 (with attached retainer 12) and the receiver 10prior to fixing of the shank 4 in a desired position with respect to thereceiver 10. The shank upper portion 8 has an outer, convex andsubstantially spherical lower surface 134 that extends outwardly andupwardly from the neck 126 and terminates at a substantially planarledge or shelf 136 that is annular and disposed perpendicular to theshank axis A. The spherical lower surface 134 has an outer radius thatis the same or substantially similar to an outer radius of the retainer12 as will be described in greater detail below, the surface 134 as wellas the retainer 12 outer surface participating in the ball and socketjoint formed by the shank 4 and attached retainer 12 within thepartially spherical surface defining an inner cavity of the receiver 10.Extending upwardly from the ledge 136 is a cylindrical surface 138, thesurface 138 having a radius that is smaller than the radius of the lowerspherical surface 134. Extending outwardly from the cylindrical surface138 is another annular surface or upper ledge 140 that faces toward theledge 136 and is also substantially perpendicular to the axis A. As willbe discussed in greater detail below, the lower ledge 136, cylindricalsurface 138 and upper ledge 140 cooperate to capture and fix theresilient open retainer 12 to the shank upper portion 8, prohibitingmovement of the retainer 12 along the axis A once the retainer 12 islocated between the ledges 136 and 140. Extending upwardly from theupper ledge 140 is a cylindrical surface 142 having a radius smallerthan the radius of the spherical surface 134 but larger than the radiusof the cylindrical surface 138. Extending upwardly from the surface 142is an upper partially spherical or domed surface 144. The sphericalsurface 144 has an outer radius configured for sliding cooperation andultimate frictional mating with a substantially spherical concavesurface of the compression insert 14 that has the same or substantiallysimilar radius as the surface 144. The radius of the surface 144 issmaller than the radius of the lower spherical surface 134. Located nearor adjacent to the surface 144 is an annular top surface 146. In theillustrated embodiment a bevel 147 extends about the spherical surface144 and is located between the spherical surface 144 and the annularplanar top surface 146.

A counter sunk substantially planar base or seating surface 149partially defines an internal drive feature or imprint 150. Theillustrated internal drive feature 150 is an aperture formed in the topsurface 146 and has a multi-lobular or star-shaped aperture, such asthose sold under the trademark TORX, the aperture designed to receive atool (not shown) of an Allen wrench type, into the aperture for rotatingand driving the bone screw shank 4. It is foreseen that such an internaltool engagement structure may take a variety of tool-engaging forms andmay include one or more apertures of various shapes, such as a pair ofspaced apart apertures or hex shape, or other geometric shape. The seator base 149 of the drive feature 150 is disposed perpendicular to theaxis A with the drive feature 150 otherwise being coaxial with the axisA. In operation, a driving tool is received in the internal drivefeature 150, being seated at the base 149 and engaging the faces of thedrive feature 150 for both driving and rotating the shank body 6 intothe vertebra 17, either before the shank 4 is attached to the receiver10 as shown in FIG. 42 or after the shank 4 is attached to the receiver10, with the shank body 6 being driven into the vertebra 17 with thedriving tool extending into the receiver 10.

The shank 4 shown in the drawings is cannulated, having a small centralbore 151 extending an entire length of the shank 4 along the axis A. Thebore 151 is defined by an inner cylindrical wall of the shank 4 and hasa circular opening at the shank tip 128 and an upper openingcommunicating with the internal drive 150 at the surface 149. The bore151 is coaxial with the threaded body 6 and the upper portion 8. Thebore 151 provides a passage through the shank 4 interior for a length ofwire (not shown) inserted into the vertebra 17 prior to the insertion ofthe shank body 6, the wire providing a guide for insertion of the shankbody 6 into the vertebra 17.

To provide a biologically active interface with the bone, the threadedshank body 6 may be coated, perforated, made porous or otherwisetreated. The treatment may include, but is not limited to a plasma spraycoating or other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth. Certain metal coatings act as ascaffold for bone ingrowth. Bio-ceramic calcium phosphate coatingsinclude, but are not limited to: alpha-tri-calcium phosphate andbeta-tri-calcium phosphate (Ca₃(PO₄)₂), tetra-calcium phosphate(Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, isdesirable as hydroxyapatite is chemically similar to bone with respectto mineral content and has been identified as being bioactive and thusnot only supportive of bone ingrowth, but actively taking part in bonebonding.

With particular reference to FIGS. 18-25, the receiver 10 has agenerally U-shaped appearance with a partially discontinuoussubstantially cylindrical inner profile and a partially cylindrical andpartially faceted outer profile. The receiver 10 has an axis of rotationB that is shown in FIG. 18 as being aligned with and the same as theaxis of rotation A of the shank 4, such orientation being desirable, butnot required during assembly of the receiver 10 with the shank 4. Afterthe receiver 10 is pivotally attached to the shank 4, either before orafter the shank 4 is implanted in a vertebra 17, the axis B is typicallydisposed at an angle with respect to the axis A, as shown, for example,in FIGS. 54-58.

The receiver 10 includes a substantially cylindrical base 158 integralwith a pair of opposed upstanding arms 160. A cavity, generally 161, islocated within the base 158. The arms 160 form a cradle and define aU-shaped channel 162 with an upper opening, generally 163, and aU-shaped lower seat 164, the channel 162 having a width for operablysnugly receiving the rod 21 between the arms 160. The channel 164communicates with the base cavity 161. Each of the arms 160 has aninterior surface, generally 166 that has a cylindrical profile andfurther includes a partial helically wound guide and advancementstructure 168 extending radially inwardly from the surface 166 andlocated adjacent top surfaces 169 of each of the arms 160. In theillustrated embodiment, the guide and advancement structures 168 areeach in the form of a partial helically wound interlocking flange formconfigured to mate under rotation with the dual start closure structure18. Thus, unlike single start advancement structures, the helical forms168 on the opposing arm surfaces 166 that are configured to mate withthe dual start closure top 18 are reverse or flipped images of oneanother, the structures 168 on each arm 160 being aligned with respectto the receiver axis B, so that each closure structure start and aresimultaneously engaged and captured at each arm 160 at the same time.

The arms 160 further include an opposed pair of vertically extendingouter grooves, generally 174, running substantially parallel to thereceiver axis B that are centrally formed in outer curved (illustratedas faceted, both curved and planar) surfaces 176. Each groove 174 runscentrally from the respective arm top surface 169 and terminates at athrough aperture 177. Each aperture 177 extends through the respectivearm surface 176 and also through the respective interior arm surface 166and is located spaced from the receiver base 158. Each groove 174 has anupper opening partially defined by a pair of opposed surfaces 179 and asubstantially planar outer wall surface 181 extending between thesurfaces 179. The planar wall surface 181 terminates at the top armsurface 169 and at a lower surface 182 partially defining the aperture177. The illustrated opposed surfaces 179 are parallel and extend belowthe lower surface 182, partially defining the through aperture 177. Theopposed surfaces 179 are sized to receive portions of an elongate tool(not shown) for locking and unlocking the insert 14 with respect to thereceiver as will be described in greater detail below. In someembodiments, the surfaces 179 may be disposed at a slight angle withrespect to each other, forming a dovetail-like space for maintaining aclose relationship between an elongate tool (not shown) that enters intothe groove 174 at the arm top surface 169 and is slidingly receivedbetween the surfaces 179. The surfaces 179 terminate at a lower surface183 that also partially defines the through aperture 177. The surface183 is substantially perpendicular to the surfaces 179. Thus, theillustrated through aperture 177 located below each of the grooves 174is substantially the same width as the groove 174 there-above, resultingin the aperture 177 having a substantially rectangular profile. Thethrough apertures 177 are sized and shaped for receiving tooling andportions of the compression insert 14 as will be described in greaterdetail below.

With particular reference to FIGS. 19, 22, 24, and 41, formed in the armsurfaces 176 and located on either side of the through apertures 177 arelateral crimping apertures 186. The four crimping apertures 186 aresubstantially circular in profile and do not extend completely throughthe respective arms 160, but rather terminate at a location between thearm outer surface 176 and the interior surface 166 to provide a crimpingportion or wall 187. The crimping portions or walls 187 are sized andshaped for pressing or crimping some or all of the wall materialinwardly onto front and rear surfaces of the insert 14 to prohibitrotation and misalignment of the insert 14 with respect to the receiver10 as will be described in greater detail below.

The receiver 10 is a one-piece or integral structure and is devoid ofany spring tabs or collet-like structures. Preferably the insert and/orreceiver are configured with structure for blocking rotation of theinsert with respect to the receiver, such as the crimp walls 187, butallowing some up and down movement of the insert with respect to thereceiver during the assembly and implant procedure. Also formed in eachouter arm surface 176 near the top surface 169 is an undercut toolreceiving and engaging groove 189. Some or all of the apertures andgrooves described herein, including, but not limited to grooves 174,apertures 177, and grooves 189 may be used for holding the receiver 10during assembly with the insert 14, the retainer 12 and the shank 4;during the implantation of the shank body 6 into a vertebra when theshank is pre-assembled with the receiver 10; during assembly of the boneanchor assembly 1 with the rod 21 and the closure structure 18; andduring lock and release adjustment of inserts according to the inventionwith respect to the receiver 10, either into or out of frictionalengagement with the inner surfaces of the receiver 10 as will bedescribed in greater detail below. It is foreseen that tool receivinggrooves or apertures may be configured in a variety of shapes and sizesand be disposed at other locations on the receiver arm 160 outersurfaces 176 and/or inner surfaces 166 as well as surfaces defining thebase 158.

Returning to the interior arm surfaces, generally 166, of the receiverarms 160, located below the discontinuous guide and advancementstructure 168 is a discontinuous cylindrical surface 190 partiallydefining a run-out feature for the guide and advancement structure 168.Adjacent to and above the surface 190 is a discontinuous upper annularceiling surface 191. The upper annular surface 191 includes the surface182 that partially defines the aperture 177 and also includes bottomsurfaces of the guide and advancement structure 168. Also adjacent toand below the surface 190 is a discontinuous annular surface or step 192that in turn is adjacent to a discontinuous frusto-conical surface 193that extends from the surface 192 inwardly toward the receiver centralaxis B. Adjacent the surface 193 is another substantially cylindricaldiscontinuous surface 194 that may in some embodiments runfrusto-conical either toward or away from the axis B, depending upon,for example, clearance requirements for the top loading of assemblycomponents, such as the retainer and a compression insert or inserts andalso modifying (enlarging or reducing) a thickness for the crimpingwalls 187, if desired. In the current embodiment, the surface 194terminates at a small discontinuous ledge or lip 195 directed inwardlytoward the axis B. The through apertures 177 extend through both thecylindrical surfaces 190 and the surfaces 193 and 194. A cylindricalsurface 196 is adjacent to and runs downwardly from the lip 195 towardsthe base cavity 161. A lower portion of the cylindrical surface 196 iscontinuous and thus partially defines the base cavity 61. Thecylindrical surface 196 has a diameter smaller than a diameter of thecylindrical surface 190, but larger than a diameter of the surface 194.The receiver inner arm surfaces 166 may further include other sloped,stepped or chamfered surfaces between the cylindrical surfaces 190, 194,and 196 as desired for ease in assembly of the other top loadedcomponents.

With particular reference to FIGS. 23-25, the continuous portion of theinner cylindrical surface 96 terminates at a downwardly sloping, annularledge surface 197 that extends from the surface 196 and runs inwardlytoward the receiver axis B. The surface 197 terminates at asubstantially cylindrical surface 198. The surface 198 terminates atanother annular surface 199 that faces a lower portion of the receivercavity 161. The surfaces 197, 198, and 199 form an abutment or ceilingstop for the retainer 12 as will be described in greater detail below.The ceiling surface 199 runs substantially perpendicular to the axis B.Cut or otherwise formed into the surfaces 197, 198, and 199 under one ofthe arms 160 is a curved c-shaped notch, creating a substantiallycylindrical surface 200 having a radius greater than a radius of thesurface 198, the opening partially defined by the surface 200 providingclearance within the assembly 1, allowing the retainer 12 to move abovethe surface 197 when the shank 4 and attached retainer 12 are pivoted ata favored angle, for example, as shown in FIG. 58 and discussed in moredetail below.

As stated above, the surface 199 is substantially annular and defines anupper ceiling or stop of a retainer 12 expansion portion or chamber ofthe inner cavity 161 that is further defined by a substantiallyspherical surface 202 that is adjacent to the surface 199. The surface202 partially defines a recess that is sized and shaped to receive theretainer 12 as it expands around the shank upper portion 8 as the shank8 is moved upwardly toward the channel 162 during assembly. Locatedbelow and adjacent to the spherical surface 202 is another curvedsurface 203 extending downwardly and inwardly toward the axis B. Thesurface 203 is illustrated as spherical, but in some embodiments thesurface may be frusto-conical. The surface 203 is a seating surface forthe retainer 12, the surface 203 slidingly receiving the retainer 12until the retainer is frictionally locked against the surface 203 whendownward pressure is placed on the shank 4 by the insert 14. Acylindrical surface 204 is adjacent the spherical surface 203 and anoutwardly flaring surface 205, illustrated as frusto-conical, spansbetween the cylindrical surface 204 and a bottom surface 206 of thereceiver 10. The surface 205 communicating with the bottom surface 206to define a lower opening, generally 207 into the receiver base innercavity 161. The cylindrical surface 204, as well as the frusto-conicalsurface 203 are sized and shaped to be smaller than an upper outerradial dimension of the retainer 12 when the retainer 12 is fixed to theshank upper portion 8, so as to form a restriction to prevent thestructure 12 and attached shank portion 8 from passing through thecavity 161 and out the lower exterior 206 of the receiver 10 duringoperation thereof.

In various embodiments of the invention, a cut-out or aperture made ofone or more notches or curved, cupped or stepped surfaces may be cutinto or otherwise formed in a portion of the base surface 206, as wellas in portions of the surfaces 202, 203, 204, and 205, the cupped orstepped surfaces being typically located substantially centrally anddirectly below one of the arm 160. Such a cupped or stepped surface orsurfaces may be sized and shaped for providing clearance for anincreased angle of articulation between the shank 4 and the receiver 10in a particular or desired direction. In the present embodiment, onesuch arrangement of stepped surfaces, generally 208 is illustrated. Inparticular, the cut-out portion 208 includes a plurality of graduated,partially annular surfaces 209 connecting with a plurality of graduatedpartially planar and partially curved surfaces 210, the surfaces 209 and210 defining edges for gripping the shank 4 as shown, for example inFIG. 58. The cut-out 208 is located directly below the cut-out portion200 that provides clearance for the retainer 12 during such a favoredangle pivoting of the shank 4 and attached retainer 12.

With particular reference to FIGS. 18 and 26-29, the open retainer 12that operates to capture the shank upper portion 8 within the receiver10 has a central axis C that is operationally the same as the axis Aassociated with the shank 4 when the shank upper portion 8 and theretainer 12 are installed within the receiver 10. The retainer 12 ismade from a resilient material, such as a stainless steel or titaniumalloy, so that the retainer 12 may be expanded during assembly as willbe described in greater detail below. However, because there is littleor no need to compress the retainer 12 during assembly, the opening orslit that allows for expansion of the retainer 12 is designed to be verynarrow, advantageously providing substantial or almost full surfacecontact between the retainer and the shank upper portion 8 and alsobetween the retainer and the receiver seating surface 203.

The retainer 12 has a central channel or hollow through bore, generally221, that passes entirely through the structure 12 from a top surface222 to a bottom surface 224 thereof. The bore 221 is primarily definedby a discontinuous inner cylindrical surface 225 that runs from the topsurface 222 to the bottom surface 224. In some embodiments of theinvention, notches or grooves may be formed in the inner and/or bottomsurfaces to more evenly distribute stress across the entire retainerduring expansion thereof. The retainer 12 further includes an outersubstantially spherical surface 227 running between the top surface 222and the bottom surface 224, the surface 227 has an identical orsubstantially similar radius as the receiver seating surface 203 andalso the shank lower spherical surface 134. The resilient retainer 12further includes first and second end surfaces, 230 and 231 disposed inspaced relation to one another when the retainer is in a neutral state.Both end surfaces 230 and 231 are disposed substantially perpendicularto the top surface 222 and the bottom surface 224. The embodiment shownin FIGS. 26-29 illustrates the surfaces 230 and 231 as substantiallyparallel, however, it is foreseen that it may be desirable to orient thesurfaces obliquely or at a slight angle to the top and bottom surfaces.

With particular reference to FIGS. 18 and 30-36, the locking compressioninsert 14 is illustrated that is sized and shaped to be received by anddown-loaded into the receiver 10 at the upper opening 166. Thecompression insert 14 has an operational central axis that is the sameas the central axis B of the receiver 10. In operation, the insertadvantageously frictionally engages the bone screw shank upper portion 8as well as engaging the receiver 10 in an interference fit engagement,locking the shank 4 in a desired angular position with respect to thereceiver 10 that remains in such locked position even if, for example, arod and closure top are later removed and the rod is replaced withanother rod or other longitudinal connecting member or member component,such as a sleeve of a tensioned cord connecting member. Such lockedposition may also be released by the surgeon if desired with insertengaging tools (not shown). In some embodiments of the invention, analternative insert is provided that does not have the receiverinterference fit feature, but is otherwise substantially similar to theinsert 14. Such an insert includes outer surfaces that are slidinglyreceived along the receiver 10 surfaces defining the arms 160 and thecavity 161. The locking insert 14 (as well as the non-lockingalternative insert not shown) is preferably made from a solid resilientmaterial, such as a stainless steel or titanium alloy, so that portionsof the insert 14 may be grasped, pinched or pressed, if necessary, andun-wedged from the receiver 10 with a release tool (not shown).

The locking compression insert 14 includes a body 256.with cylindricalsurfaces of a variety of diameters as well as planar surfaces andchamfers and cut-outs to provide clearance between the insert 14 and theretainer 12 during various steps of assembly as well as when theassembly 1 is in a final locked position. The body 256 is integral witha pair of upstanding arms 257. Located between the arms 257, the body256 has an outer partial cylindrical surface 258. Each arm outer surfaceis substantially cylindrical in profile but is made from a variety offacets or faces as well as cut-outs to provide for clearance with othercomponents of the assembly 1.

Located on the body 256 below each upstanding arm 257 is a substantiallycylindrical interference fit surface or band 159 that extends outwardlyfrom and between an upper cylindrical surface 260 and a lowercylindrical surface 261. The lower surface 261 is adjacent to an annularbottom surface 264 of the insert 14. Each upper cylindrical surface 260partially defines one of the insert arms 257. The interference fit band159 runs substantially parallel to the bottom surface 264. A diameter ofthe insert 14 measured at the band surface 259 is larger than a diametermeasured at surfaces 260 or 261. As best shown in FIG. 36, in theillustrated embodiment, the bottom surface 264 is disposed at an anglewith respect to the lower surface 261, but may be perpendicular to thelower surface 261 in other embodiments. The insert 14 further includessubstantially planar arm top surfaces 265 located opposite the bottomsurface 264. The arms 257 are each further defined by substantiallyplanar front and rear surfaces 266 that run from the top surfaces 265 tothe bottom surface 264. At the bottom surface 264, the front and rearsurfaces 266 are narrow due to clearance cut-outs 267 located at eachcorner of the insert 14. Each arm 257 also includes an outwardlyextending wing, generally 268 located centrally on and extendingoutwardly from an upper cylindrical surface 269 of the arm 257, thesurface 269 being adjacent to the arm top surface 265. Each arm topsurface 265 also extends along the respective wing 268 to asubstantially cylindrical outer surface 270. Each wing is also definedby a lower surface 271 and opposed planar side surfaces 272, the uppersurfaces 265 and the lower surfaces 271 being substantially parallel toone another. The juncture between the planar side surfaces 272 and thecylindrical surface 270 may include one or more chamfered, planed, orotherwise angled or curved surface to aid in rotational assembly of theinsert 14 within the receiver 10. The opposed side surfaces 272generally span between top and bottom surfaces 265 and 271 respectively,of each wing 268, the side surfaces 272 being substantiallyperpendicular to adjacent top and bottom surfaces 265 and 271. Thecylindrical surfaces 270 are sized and shaped for sliding rotationwithin the receiver arm cylindrical surfaces 190 during assembly of theinsert 14 with the receiver 10 as will be described in greater detailbelow. The illustrated wings 268 include indicator stripes 273 thatprovide a surgical staff with an indication of the location of theinsert 14 with respect to the receiver 10 during surgery. For example,the location of the stripe 273 with respect to the receiver 10 indicateswhether the insert 14 is in a non-floppy, but movable, frictionalengagement with the shank head 8 or whether the insert 14 is fullylocked down on the shank head 8. The indicator stripes 273 areconveniently located on the wing cylindrical surface 270 that is visiblewhen the wings 268 are extending through the receiver apertures 177.

Returning to the inner surfaces of the insert 14, a through bore,generally 275, is disposed primarily within and through the body 256 andcommunicates with a generally U-shaped through channel formed by asaddle surface 278 that is substantially defined by the upstanding arms257. Near the top surfaces 265, the saddle surface 278 is substantiallyplanar. The saddle 278 has a curved lower seat 279 sized and shaped toclosely, snugly engage the rod 21 or other longitudinal connectingmember. It is foreseen that an alternative embodiment may be configuredto include planar holding surfaces that closely hold a square orrectangular bar as well as hold a cylindrical rod-shaped, cord, orsleeved tensioned cord longitudinal connecting member. A pair ofopposed, inwardly facing grooves or apertures 280 are located in thesaddle 278 beginning near a juncture of the substantially planar upperportion of the saddle 278 and extending toward the curved lower seat279. The grooves 280 are sized and shaped to receive tooling forrotation, locking, unlocking and other manipulation of the insert 14.

The bore, generally 275, is substantially defined at the body 256 by aninner cylindrical surface 282 that communicates with the seat 279 andalso communicates with a lower concave, radiused or otherwise curvedportion 284, that in some embodiments may include shank grippingsurfaces or ridges, the surface portion 284 generally having a radiusfor closely mating with the surface 144 of the shank upper portion 8.The portion 284 terminates at the base surface 264. It is foreseen thatthe lower shank engaging portion 284 may additionally or alternativelyinclude a roughened or textured surface or surface finish, or may bescored, knurled, or the like, for enhancing frictional engagement withthe shank upper portion 8. Formed in a portion of the surface 284 and ina portion of the bottom surface 264 is a notch 286 sized and shaped toreceive a portion of the retainer 12 when the shank 4 and attachedretainer 12 are pivoted into a favored angle position as shown, forexample, in FIG. 58. The notch 286 is located directly beneath one ofthe arms 257 and has a geometry for receiving a portion of the top 222and outer spherical surface 227 of the retainer 12 when the shank upperportion 8 is fully locked into place by the insert surface 284 and theshank 4 is pivoted toward the receiver cut-out 208.

The compression insert 14 through bore 275 is sized and shaped toreceive a driving tool (not shown) therethrough that engages the shankdrive feature 146 when the shank body 6 is driven into bone with thereceiver 10 attached. Also, in some locking embodiments of theinvention, the bore receives a manipulation tool (not shown) used forreleasing the insert 14 from a locked position with the receiver 10, thetool pressing down on the shank head 8 and also gripping the insert 14at the apertures 280, or with other tool engaging features. Each of thearms 257 and the insert body 256 may include more surface features, suchas cut-outs notches, bevels, etc. to provide adequate clearance forinserting the insert 14 into the receiver and cooperating with theretainer 12 during the different assembly steps as will be described ingreater detail below.

The insert body 256 cylindrical surface 258 has a diameter slightlysmaller than a diameter between crests of the guide and advancementstructure 168 of the receiver 10, allowing for top loading of thecompression insert 14 into the receiver opening 163, with the arms 257of the insert 14 being located between the receiver arms 160 duringinsertion of the insert 14 into the receiver 10 as shown, for example,in FIG. 38. Once the arms 257 of the insert 14 are generally locatedbeneath the guide and advancement structure 168, the insert 14 isrotated into place about the receiver axis B with the wings 268 enteringthe receiver groove formed by the cylindrical surface 190, the adjacentupper annular surface 191 and the adjacent lower annular surface 192until the wings 268 are located in the apertures 177 as will bedescribed in greater detail below.

With reference to FIGS. 18 and 48-50, the illustrated elongate rod orlongitudinal connecting member 21 (of which only a portion has beenshown) can be any of a variety of implants utilized in reconstructivespinal surgery, but is typically a cylindrical, elongate structurehaving the outer substantially smooth, cylindrical surface 22 of uniformdiameter. The rod 21 may be made from a variety of metals, metal alloysand deformable and less compressible plastics, including, but notlimited to rods made of elastomeric, polyetheretherketone (PEEK) andother types of materials, such as polycarbonate urethanes (PCU) andpolyethylenes.

Longitudinal connecting members for use with the assembly 1 may take avariety of shapes, including but not limited to rods or bars of oval,rectangular or other curved or polygonal cross-section. The shape of theinsert 14 may be modified so as to closely hold the particularlongitudinal connecting member used in the assembly 1. Some embodimentsof the assembly 1 may also be used with a tensioned cord. Such a cordmay be made from a variety of materials, including polyester or otherplastic fibers, strands or threads, such as polyethylene-terephthalate.Furthermore, the longitudinal connector may be a component of a longeroverall dynamic stabilization connecting member, with cylindrical orbar-shaped portions sized and shaped for being received by thecompression insert 14 of the receiver having a U-shaped, rectangular- orother-shaped channel, for closely receiving the longitudinal connectingmember. The longitudinal connecting member may be integral or otherwisefixed to a bendable or damping component that is sized and shaped to belocated between adjacent pairs of bone screw assemblies 1, for example.A damping component or bumper may be attached to the longitudinalconnecting member at one or both sides of the bone screw assembly 1. Arod or bar (or rod or bar component) of a longitudinal connecting membermay be made of a variety of materials ranging from deformable plasticsto hard metals, depending upon the desired application. Thus, bars androds of the invention may be made of materials including, but notlimited to metal and metal alloys including but not limited to stainlesssteel, titanium, titanium alloys and cobalt chrome; or other suitablematerials, including plastic polymers such as polyetheretherketone(PEEK), ultra-high-molecular weight-polyethylene (UHMWP), polyurethanesand composites, including composites containing carbon fiber, natural orsynthetic elastomers such as polyisoprene (natural rubber), andsynthetic polymers, copolymers, and thermoplastic elastomers, forexample, polyurethane elastomers such as polycarbonate-urethaneelastomers.

Preferably, the receiver 10, the retainer 12 and the compression insert14 are assembled at a factory setting that includes tooling for holding,alignment and manipulation of the component pieces, as well as crimpinga portion of the receiver 10 toward the insert 14. In somecircumstances, the shank 4 is also assembled with the receiver 10, theretainer 12 and the compression insert 14 at the factory. In otherinstances, it is desirable to first implant the shank 4, followed byaddition of the pre-assembled receiver, retainer and compression insertat the insertion point (see, e.g., FIG. 42). In this way, the surgeonmay advantageously and more easily implant and manipulate the shanks 4,distract or compress the vertebrae with the shanks and work around theshank upper portions or heads without the cooperating receivers being inthe way. In other instances, it is desirable for the surgical staff topre-assemble a shank of a desired size and/or variety (e.g., surfacetreatment of roughening the upper portion 8 and/or hydroxyapatite on theshank 6), with the receiver, retainer and compression insert. Allowingthe surgeon to choose the appropriately sized or treated shank 4advantageously reduces inventory requirements, thus reducing overallcost.

Pre-assembly of the receiver 10, retainer 12 and compression insert 14is shown in FIGS. 37-41. With particular reference to FIG. 37, first theretainer 12 is inserted into the lower receiver opening 207, leadingwith the outer surface 227, the top surface 222 slightly angled to faceupwardly and toward one arm 160 that is located above the stepped,cut-out 208. The retainer 12 is then moved upwardly and at an angletoward the annular ceiling surface 199 located opposite the cut-outsurface 200 and then past the stepped cut-out 298 in such an angled andupward manner into the chamber 161, followed by tilting the retainer 12such that the top surface 222 is moved into a position within thereceiver cavity 161 axially aligned with the receiver axis B and spacedfrom the surface 199. Then the retainer 12 is allowed to drop until theretainer spherical surface 227 is seated on the receiver sphericalsurface 203 as shown in FIG. 38.

Also with reference to FIG. 38 and with further reference to FIGS. 39and 40, the. compression insert 14 is then downloaded into the receiver10 through the upper opening 163 with the bottom surface 264 initiallyfacing the receiver arm top surfaces 169 and the insert arms 257 locatedbetween the opposed receiver arms 160. The insert 14 is then loweredtoward the channel seat 164 until the insert 14 arm upper surfaces 265are adjacent the receiver arm inner surfaces located below the guide andadvancement structures 168. Thereafter, the insert 14 is rotated in aclockwise or counter-clockwise manner about the receiver axis B untilthe upper arm surfaces 265 are directly below the guide and advancementstructure 168 of each arm as illustrated in FIG. 40 with the U-shapedchannel 278 of the insert 14 aligned with the U-shaped channel 162 ofthe receiver 10. In some embodiments, the insert arms 257 may need to becompressed slightly during rotation to clear inner surfaces of thereceiver arms 160. As the insert 14 is rotated about the axis B, theinsert wings, generally 268 slidingly rotate within the circular grooveformed by the receiver surfaces 190, 191, and 192.

With particular reference to FIGS. 40 and 41, at this time, the fourcrimping wall portions 187 are pressed inwardly towards the insert 14and crimping wall material thus engages the insert near front and rearsurfaces 266 thereof, specifically at the four surfaces or facets 267 asbest shown in FIG. 41. The crimping wall material of the wall 187pressing against the insert 14 at a total of four locations therebyprohibits the insert 14 from rotating with respect to the receiver axisB. At this time, there can be some upward and downward movement of theinsert 14, but such movement is limited as the upper wall 182 definingthe receiver aperture 177 (that is also the surface 191) stops furtherupward movement of the insert wings 268. Downward movement of the insert14 is prohibited by the bands 259 resting on receiver ledge surface 195adjacent the cylindrical surface 196. The retainer 12 and the insert 14are now in a desired position for shipping as an assembly along with theseparate shank 4 and also ready for assembly with the shank 4 either atthe factory, by surgery staff prior to implantation, or directly upon animplanted shank 4 as will be described herein.

As illustrated in FIG. 42, the bone screw shank 4 or an entire assembly1 made up of the assembled shank 4, receiver 10, retainer 12 andcompression insert 14, is screwed into a bone, such as the vertebra 17,by rotation of the shank 4 using a suitable driving tool (not shown)that operably drives and rotates the shank body 6 by engagement thereofat the internal drive 150. Specifically, the vertebra 17 may bepre-drilled to minimize stressing the bone and have a guide wire (notshown) inserted therein to provide a guide for the placement and angleof the shank 4 with respect to the vertebra. A further tap hole may bemade using a tap with the guide wire as a guide. Then, the bone screwshank 4 or the entire assembly 1 is threaded onto the guide wireutilizing the cannulation bore 151 by first threading the wire into theopening at the bottom 128 and then out of the top opening at the drivefeature 150. The shank 4 is then driven into the vertebra using the wireas a placement guide. It is foreseen that the shank and other bone screwassembly parts, the rod 21 (also having a central lumen in someembodiments) and the closure top 18 having the central bore 62 can beinserted in a percutaneous or minimally invasive surgical manner,utilizing guide wires. When the shank 4 is driven into the vertebra 17without the remainder of the assembly 1, the shank 4 may either bedriven to a desired final location or may be driven to a locationslightly above or proud to provide for ease in assembly with thepre-assembled receiver, compression insert and retainer.

With further reference to FIG. 42, the pre-assembled receiver, insertand retainer are placed above the shank upper portion 8 until the shankupper portion is received within the opening 207. With particularreference to FIGS. 43-45, as the shank upper portion 8 is moved into theinterior 161 of the receiver base, the shank upper portion 8 pressesupwardly against the retainer 12 in the recess partially defined by thespherical surface 202. As the portion 8 continues to move upwardlytoward the channel 162, the shank surface 144 forces outward movement ofthe retainer 12 towards the surface 202 in the receiver expansionchamber or area as the shank 4 presses the retainer 12 up against thereceiver annular ledge surface or ceiling 199. The retainer 12 initiallyexpands about the shank upper spherical surface 144 and then slidesalong the cylindrical surface 142, and finally snapping or popping intothe recessed cylindrical surface 138, the surface 225 of the retainer 12fully contacting and frictionally engaging the cylindrical surface 138between the shank lower ledge 136 and the upper ledge 140. At this time,the retainer 12 is in a neutral or slightly expanded state, fullysnapped onto the shank upper portion 8 with both the retainer 12 andshank upper portion 8 in pivotal relation with the receiver 10.

With reference to FIG. 46, the shank 4 and attached retainer 12 are thenmoved downwardly into a desired position with the retainer seated on thesurface 203. With reference to FIG. 47, the insert 14 may be presseddownwardly by a tool (not shown) entering at the receiver grooves 174,for example, and pressing down on the insert wings 268, to result in africtional engagement between the insert inner spherical surface 284 andthe shank upper domed surface 144 to an extent that the shank ispivotable with respect to the receiver, but in a non-floppy manner. Theinsert 14 remains in such position due to interference fit engagementbetween the insert outer band surfaces 259 and the receiver cylindricalsurfaces 196. Alternatively, the insert 14 may be pushed into suchinterference fit by a rod 21 and closure top 18. Typically, tools arefirst used to provide the non-floppy arrangement between the insert 14and the shank head 8, followed by performing a locking engagementutilizing the rod 21 and closure top 18 as shown in FIG. 48. In someembodiments, when the receiver 10 is pre-assembled with the shank 4, theentire assembly 1 may be implanted after the insert 14 is pressed intonon-floppy frictional engagement with the shank head 8 by inserting thedriving tool (not shown) into the receiver and the shank drive 150 androtating and driving the shank 4 into a desired location of the vertebra17.

Again, with reference to FIG. 48 and also FIG. 49, the rod 21 iseventually positioned in an open or percutaneous manner in cooperationwith the at least two bone screw assemblies 1. The closure structure 18is then inserted into and advanced between the arms 160 of each of thereceivers 10. The closure structure 18 is rotated, using a tool engagedwith the inner drive 56 until a selected pressure is reached at whichpoint the rod 21 engages the U-shaped seating surface 278 of thecompression insert 14, further pressing the insert spherical surface 284against the shank spherical surface 144, pressing the shank upperportion 8 and attached retainer 12 into locked frictional engagementwith the receiver 10. With specific reference to FIGS. 3, 48, and 49, asthe multi-start closure structure 18 rotates and moves downwardly intothe respective receiver 10, the rim 60 engages and penetrates the rodsurface 22, the closure structure 18 pressing downwardly against andbiasing the rod 21 into compressive engagement with the insert 14 thaturges the shank upper portion 8 and attached retainer 12 into lockingengagement with the receiver, the retainer 12 spherical surface 227frictionally abutting the spherical seating surface 203 of the receiver10. For example, about 80 to about 120 inch pounds of torque on theclosure top may be applied for fixing the bone screw shank 6 withrespect to the receiver 10. Also, for example, with reference to FIGS.52-58, when the shank 4 is disposed at an angle with respect to thereceiver 10, the lower spherical surface 134 of the shank upper portion8 may also be in frictional engagement with a portion of the receiverspherical seating surface 203. The retainer 12 may also expand slightlyupon locking, providing a full and secure frictional locking engagementwith the receiver at the surface 203.

If removal of the rod 21 from any of the bone screw assemblies 1 isnecessary, or if it is desired to release the rod 21 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 56 on the closure structure 18to rotate and remove such closure structure from the cooperatingreceiver 10. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

With further reference to FIG. 49 and also with reference to FIG. 50, atthis time, the closure top 18 may be loosened or removed and/or the rod21 may be adjusted and/or removed and the frictional engagement betweenthe insert 14 and the receiver 10 at the receiver surface 196 willremain locked in place, advantageously maintaining a locked angularposition of the shank 4 with respect to the receiver 10. Thus, at thistime, another rod, such as the deformable rod 21′ and cooperatingalternative multi-start closure top 18′ may be loaded onto the alreadylocked-up assembly to result in an alternative assembly. It is notedthat the closure drive 56′ may advantageously be made smaller than thedrive of the closure 18, such that the deformable rod 21′ is not undulypressed or deformed during assembly since the polyaxial mechanism isalready locked.

With reference to FIGS. 51-58, prior to locking the insert 14 againstthe shank head 8, the shank 4 may be pivoted to a plurality ofpotentially desirable positions with respect to the receiver 10,followed by locking of the polyaxial mechanism by fully mating themulti-start closure top 18 with the receiver 10. For example, differentangular or articulated positions of the shank 4 with respect to thereceiver 10 are shown, some making full use of the stepped cut-out 208and the c-shaped groove forming the surface 200 of the receiver and/orthe notch 286 of the insert 14. For reference, FIG. 51 illustrates azero degree relationship between the shank 4 and the receiver 10. Inother words, the axis A of the shank is aligned with the axis B of thereceiver. FIG. 52 shows the shank 4 pivoted laterally of the receivercut-out portion 208 in an eighteen degree cephalic relationship. FIG. 53shows the shank 4 pivoted away from the receiver cut-out portion 208 inan eighteen degree caudal relationship. FIG. 54 illustrates the shank 4being pivoted with respect to the receiver 10 at an eighteen degreelateral relationship. FIG. 55 shows the shank 4 pivoted toward thereceiver cut-out portion 208 at a forty-two degree medial by eightdegree cephalic relationship. FIG. 56 shows the shank 4 pivoted towardthe receiver cut-out portion 208 at a forty-two degree medialrelationship. FIGS. 57 and 58 show the shank 4 pivoted toward thereceiver cut-out portion 208 at a forty-two degree medial by eightdegree caudal relationship. FIG. 58 also shows that in such a pivotedrelationship between the shank 4 and the receiver 10, a portion of theretainer 12 moves past the receiver surface 200 and is received by thenotch 286 in the insert 14.

With reference to FIGS. 9 and 10, an alternative closure top 18′ isshown that is almost identical to the closure top 18. However, the top18′ differs from the top 18 in that the top 18′ includes a break-offhead 70′ that further includes a top surface 72′ having tooling notches73′, an outer faceted driving surface 74′, illustrated as having ahex-shaped profile, and an inner bore 76′. Otherwise, the closure top18′ includes a body 40′, a first helical form 42′, a second helical form43′, a body top surface 54′, a body internal drive 56′, a base 58′, arim 60′, a cannulation bore 62′ and a drive base surface 63′ that is thesame or substantially similar to the respective body 40, first helicalform 42, second helical form 43, body top surface 54, internal drive 56,base 58, rim 60, cannulation bore 62 and drive base surface 63previously described herein with respect to the closure top 18. Thebreak-off head 70′ is integral with the body 40′ at the body top surface54′. The inner bore 76′ communicates with the inner drive 56′ and thecannulation bore 62′. The break-off head 70′ is designed to allow suchhead 70′ to break from the body 40′ at or near the top surface 54′ at apreselected torque, for example, 70 to 140 inch pounds, when ahex-shaped tool (not shown) engages the outer surfaces 74′ and drivesthe closure structure 18′ into the receiver 10 as shown in FIG. 9. Theinner drive 56′ is used for disassembly or loosening of the closure 18′from the receiver 10, and re-tightening, if needed.

With reference to FIG. 11, another alternative multi-start closure top318 is shown that is almost identical to the closure top 18 with theexception that the two flange forms 42 and 43 with respective starts 46and 47 have been replaced with square threads 342 and 343 withrespective starts 346 (not shown) and 347. Otherwise, the dual or doublestart closure top 318 includes a body 340, a body top surface 354, abody internal drive 356, a base 358, a rim 360′, a cannulation bore 362and a drive base surface 363 that is the same or substantially similarto the respective body 40, body top surface 54, internal drive 56, base58, rim 60, cannulation bore 62 and drive base surface 63 previouslydescribed herein with respect to the closure top 18. In FIG. 11, theclosure top 318 is shown partially wound into a polyaxial bone screwreceiver 310 having opposed arms 360 with inner surfaces equipped withguide and advancement structures 368 that are sized and shaped tosimultaneously closely receive and mate with the square threads 342 and343 of the double closure structure 318. Otherwise, the receiver 310 isidentical or substantially similar to the receiver 10.

With reference to FIG. 12, an alternative multi-start closure top 418 isshown that is almost identical to the closure top 18 with the exceptionthat the two flange forms 42 and 43 with respective starts 46 and 47have been replaced with reverse angle threads 442 and 443 withrespective starts 446 (not shown) and 447. Otherwise, the dual or doublestart closure top 418 includes a body 440, a body top surface 454, abody internal drive 456, a base 458, a rim 460′, a cannulation bore 462and a drive base surface 463 that is the same or substantially similarto the respective body 40, body top surface 54, internal drive 56, base58, rim 60, cannulation bore 62 and drive base surface 63 previouslydescribed herein with respect to the closure top 18. The closure top 418is shown partially wound into a polyaxial bone screw receiver 410 havingopposed arms 460 with inner surfaces equipped with guide and advancementstructures 468 that are sized and shaped to simultaneously closelyreceive and mate with the reverse angle threads 442 and 443 of thedouble start closure structure 418. Otherwise, the receiver 410 isidentical or substantially similar to the receiver 10.

With reference to FIG. 13, another alternative multi-start closure top518 is shown that is almost identical to the closure top 18 with theexception that the two flange forms 42 and 43 with respective starts 46and 47 have been replaced with v-threads 542 and 543 with respectivestarts 546 (not shown) and 547. Otherwise, the dual or double startclosure top 518 includes a body 540, a body top surface 554, a bodyinternal drive 556, a base 558, a rim 560′, a cannulation bore 562 and adrive base surface 563 that is the same or substantially similar to therespective body 40, body top surface 54, internal drive 56, base 58, rim60, cannulation bore 62 and drive base surface 63 previously describedherein with respect to the closure top 18. The closure top 518 is shownpartially wound into a polyaxial bone screw receiver 510 having opposedarms 560 with inner surfaces equipped with guide and advancementstructures 568 that are sized and shaped to simultaneously closelyreceive and mate with the threads 542 and 543 of the double startclosure structure 518. Otherwise, the receiver 510 is identical orsubstantially similar to the receiver 10.

With reference to FIG. 14, another alternative multi-start closure top618 is shown that is almost identical to the closure top 18 with theexception that the two flange forms 42 and 43 with respective starts 46and 47 have been replaced with buttress threads 642 and 643 withrespective starts 446 and 447 (not shown). Otherwise, the dual or doublestart closure top 618 includes a body 640, a body top surface 654, abody internal drive 656, a base 658, a rim 660′, a cannulation bore 662and a drive base surface 663 that is the same or substantially similarto the respective body 40, body top surface 54, internal drive 56, base58, rim 60, cannulation bore 62 and drive base surface 63 previouslydescribed herein with respect to the closure top 18. The closure top 618is shown partially wound into a polyaxial bone screw receiver 610 havingopposed arms 660 with inner surfaces equipped with guide and advancementstructures 668 that are sized and shaped to simultaneously closelyreceive and mate with the buttress threads 642 and 643 of the doublestart closure structure 618. Otherwise, the receiver 610 is identical orsubstantially similar to the receiver 10.

With reference to FIGS. 15 and 16, an open receiver 710 is illustratedthat is substantially similar to the receiver 10 previously describedherein with the exception that the receiver 710 includes opposed arms760, each having an integral upstanding break-off extension 761. Eachreceiver arm 760 and integral extension 761 has an inner helically woundguide and advancement structure 768 that is sized and shaped to matewith the flange forms 42 and 43 of the dual start closure 18 previouslydescribed herein. The break-off extensions 761 are initially integralwith the respective arms 760 and are then broken off by a user after theclosure 18 has been rotatingly advanced along the arm extensions 761 andinto the channel located between the receiver arms 760. In theillustrated embodiment, in addition to an outer groove or notch 770located at or near a top surface 769 of each of the arms 760 where theextensions 761 break off from the receiver arms, illustrated inner armsurfaces include a recess or cut 771, best shown in FIG. 16, that runssubstantially horizontally. Each recess 771 is curved and elongate anddisposed somewhat cross-wise or transverse to the respective flange form768. For example, with reference to the arm 760 shown in FIG. 16, therecess 771 cuts into a weakened region, generally 780, where the arm 760joins with the respective attached adjacent extension 761, the curvedand elongate recess 771 beginning at a lower portion or location 781 ofthe flange form recess or segment and terminating at an opposed upperend location of the flange form segment, while otherwise leaving theflange form 768 intact. Stated in another way, the substantiallyhorizontally extending recess 771 cuts into both a lead portion and atrailing portion of each of the flange form segments located near anddirectly above the opposed arms 760 and substantially opposite the notch770, thus further weakening the region where the extension and the armattach, without destroying the flange form path, so that the closure 18is not derailed by the recess 771 or otherwise prohibited from movingdownwardly into the receiver channel formed between the receiver arms760.

With reference to FIG. 17, the multi-start closure 18 is showncooperating with a spinal implant receiver, such as a bone screwreceiver 10′ and a discrete, detachable guide tool 801. The elongateguide tool 801, only partially shown in FIG. 17, is typically sized forextending from the bone screw receiver 10′ upwardly to a locationoutside of a patient, the tool providing a guide channel for operablyguiding the rod 21 or other longitudinal connecting member from aposition exterior of the bone screw receiver 10′ toward and into thebone screw receiver 10′. The illustrated guide tool has opposed arms805, each arm having a helical guide and advancement structure 810thereon that is illustrated as a square thread form, but may be of othergeometry, including a flange form the same or similar to the flangeforms 168′ of the receiver 10′ that mates with the flange forms 42 and43 of the closure structure 18. Thus, the illustrated structures 810 aresized and shaped for receiving and rotating engagement with a dual startclosure. The closure 18 is shown partially wound into the receiver 10′that is identical or substantially similar to the receiver 10 with theexception of certain outer arm surface features (not shown). Thus, thereceiver 10′ includes opposed arms 160′ with inner surfaces having guideand advancement structures 168′ that are sized and shaped tosimultaneously closely receive and mate with the flange forms 42 and 43of the dual start closure structure 18. The guide tool 801 includesattachment structure for detachable attachment to the receiver 10′(notshown), that may take a variety of forms and methods, including, but notlimited to a slide-on, slide-off attachment, a snap-on, rotate offattachment, a rotate-on and rotate-off attachment, to name a few. Forexample, cooperating attachment structure for both the tool and thereceiver may be used that is disclosed in U.S. Pat. No. 7,470,279 andincorporated by reference herein. Returning to the inner helically woundguide and advancement structure 810 formed on each arm 804 of the guidetool 801, the structure 810 is sized and shaped for being aligned withthe receiver arms 160′ during removable attachment of the tool 801 withthe respective bone screw receiver 10′ so as to continue the helicalpathway for the closure 18, the structures 810 being synchronized withthe flange forms 168′ to allow for the rotation and driving transfer ofthe closure 18 from the tool 801 into the receiver 10′.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed is:
 1. A medical implant assembly comprising: a receiverhaving an upper portion with an inner surface at least partiallyconfigured as a helically wound thread extending up to a top surface ofthe receiver, and a channel configured to be attached to an elongatemember; and a plug being threaded and configured to be positioned withinthe upper portion of the receiver, the plug having an axis of rotation,a continuously helically wound thread form, and a bottom surface with anannular outer edge, the continuously helically wound thread form havinga start structure with an upper surface extending between a root and acrest of the continuously helically wound thread form, the startstructure having a leading face extending below the upper surface to alower surface of the start structure, the leading face including atleast one partial curvate surface between the root and the crest, thelower surface of the start structure being spaced apart and above theannular outer edge of the bottom surface of the plug so as to not beconnected with the annular outer edge thereof.